Recently, stricter regulation has been enforced for prevention of noise in high-frequency circuits, and an inductance element for preventing such noise came to be required, with the result that a small-sized lamination type inductor has come to be used in the field of noise prevention.
In the conventional small-sized lamination type inductor of this kind, as shown in FIGS. 9 and 10, an I-shaped conductor pattern 5 having outside lead-out electrodes 3, 4 at both ends of conductive portion 2 thereof, is printed on the surface of an intermediate ferrite sheet 1 by using conductive paste mainly composed of silver, and thereafter, the ferrite sheet 1 has laminated to the front and rear surfaces thereof plain ferrite sheets 6, 6 intended to be dummy sheets, to which plane pressure is applied and the structure is at an appropriate temperature to make it integral.
Then, after barrel finishing, conductive paste is applied to the laminated body at both end portions thereof in a manner to communicate with the lead-out electrodes 3, 4 and the paste is baked to thereby obtain outside lead-out electrodes 7, 8.
But, in such a lamination type conductor having the construction as above, a problem occurs in that, since it is small in shape and the conductive portion 2 thereof is short in length and so on, the required inductance value cannot be obtained.
Accordingly, it has been proposed that a conductor pattern constituting a coil part be printed on ferrite sheets, which are laminated to form a lamination type coil so that a coil is formed, and the inductor can be used in the noise-prevention field to thereby solve the above-described problem.
FIG. 11 shows a construction for the case where a 5.5 turn coil is constructed by using a conventional lamination type coil.
In FIG. 11, a dozen ferrite sheets 11-22 are used. Conductor patterns 31-48 are printed on either the front surface or the reverse surface, or both, of each ferrite sheet, which is laminated in turn in such a way that sheet 12 is under sheet 11, and sheet 13 is under sheet 12, and so on. End portions of each conductor pattern are positioned on top of one another, and are connected to each other to form a coil.
In FIG. 11, the conductor pattern printed on the front surface of each ferrite sheet is shown in solid lines, and the pattern on the reverse surface in broken lines. Hereafter, the same method of illustration is adopted for the drawings of this invention.
In addition, each conductor pattern is printed on a sheet while the sheet is a green ferrite sheet, which sheet is then baked to thereby obtain a finished ferrite sheet. The same is true of the present invention.
First, on the reverse side of sheet 11 is printed a conductor pattern 31 constituting an outside lead-out portion 61 and coil portion 62 equal to a 0.25 turn coil to obtain a 0.25 turn coil.
Next, sheet 12 is provided with a through hole 63 near the end portion of one side thereof, and a conductor pattern 32, intended to be a coil portion equal to a 0.25 turn coil, is printed on the front sheet surface in a manner to position the end portion thereof over the through hole 63.
The above-described conductor pattern 32 is printed in such a manner as to push printing paste into through hole 63, and the printing is followed by printing, on the reverse side of sheet 12, of the conductor pattern 33 having the same shape as that of pattern 32, with the result that the paste is pushed into the through hole 63 from both the front surface and reverse side to connect the conductor patterns 32, 33 in a sure manner to thereby obtain a 0.5 turn coil.
Each of ferrite sheets 14, 16, 18 and 20 has the same construction as that of sheet 12. Each of sheets 13, 15, 17, 19 and 21 has a conductor pattern thereon, formed in a different direction from but having the paste applied in the same way as that of sheet 12. In each conductor pattern, the same numerals are used for like parts.
In addition, the lowermost ferrite sheet 22 is provided on the surface thereof with conductor pattern 48 formed at a position at the opposite end of the sheet from that of pattern 31 on the uppermost ferrite sheet 11.
As above, ferrite sheets 11-22 on which conductor patterns are printed are laid one on top of another in the way previously described, whereby end portion 62a of conductor pattern 31 on sheet 11 is connected to portion 32a of the pattern 32 on sheet 12. Likewise, end portion 33a of conductor pattern 33 of sheet 12 is connected to portion 35a of the pattern 35 on sheet 13, so that as each sheet is laid on top of another, conductor patterns are connected to each other at the ends thereof to thereby constitute a coil.
But, with a coil in an inductor constructed as described above, a dozen ferrite sheets are required in order to obtain a 5.5 turn coil. In addition, said construction has not been satisfactory because of requirements for a large number of sheets and extensive conductor pattern printing and lack of work efficiency, workmanship, quality and because of cost.